JP2011008280A - Antireflection film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical pickup apparatus which is made to have precise compatibility with two or more types of optical disks by suitably improving an antireflection film to be used in an optical element such as an aberration correction element and which has excellent reliability.SOLUTION: The antireflection film, which is arranged on the aberration correction element being a constituent element of the optical pickup apparatus, includes at least four layers formed on a substrate of the aberration correction element. The four layers are, in the order from the substrate side, the first layer having ≥2.0 refractive index nd and 5-50 nm geometric thickness, the second layer having ≤1.5 refractive index nd and 10-200 nm geometric thickness, the third layer having ≥2.0 refractive index nd and 50-200 nm geometric thickness, and the fourth layer which includes SiO, AlOor SiON and has 50-200 nm geometric thickness.

Description

  The present invention relates to an antireflection film, and more particularly, to an improvement technique of an antireflection film provided on an optical element such as an aberration correction element of an optical pickup device compatible with a plurality of types of optical disks.

  As is well known, as an information recording medium on which information is recorded or reproduced optically, an optical disc such as a CD (Compact Disc) or a DVD (Digital Versatile Disc) is small, has a large capacity and is convenient. Attention has been paid. In recent years, compatible optical pickup devices (optical information recording / reproducing devices) that can use these different types of optical disks in a single unit have been developed.

  In this case, the DVD has a density of information about 7 times that of the CD, but in order to ensure the density of the optical disk in this way, an objective lens provided in the optical pickup device is used. By increasing the numerical aperture (NA) or using a light beam with a short wavelength, it is necessary to irradiate the optical disk with a light beam having a small irradiation diameter.

  However, when the NA of the objective lens is increased as described above or the light beam having a short wavelength is used, the influence of the aberration on the light beam by the optical disk increases, and it is difficult to improve the recording and reproduction accuracy. Become. Therefore, according to the following Patent Document 1 and Patent Document 2, it is disclosed to use an aberration correction element (referred to as an optical element in Patent Document 1) in order to reduce the influence of such aberration. Yes.

JP 2001-100194 A JP 2000-292755 A

By the way, in any of the aberration correction elements disclosed in Patent Documents 1 and 2 described above, in order to reduce the return light to the light source due to the reflection of the light beam and to transmit the light beam without loss, A prevention film is provided. As the antireflection film, a single layer film of MgF or Al ₂ O ₃ is used in the aberration correction element disclosed in Patent Document 1, and in the aberration correction element disclosed in Patent Document 2, SiO, Al ₂ O ₃ , A single layer film made of MgF ₂ or CaF ₂ is used.

  In this case, in the aberration correction element provided with the conventional antireflection film, for example, as shown in FIGS. 14 to 17 of Patent Document 2, a light beam having a wavelength of 780 nm used for a CD or a DVD is used. Although the transmittance of the light beam having a wavelength of 658 nm used is high, the transmittance of the light beam having a wavelength of 405 nm used in BD (Blue Laser Disc) is less than 70%. Therefore, the aberration correction element provided with such an antireflection film has a problem that it cannot be used as compatible with three types of optical disks of CD, DVD, and BD.

  Also, FIG. 18 of the same document describes an aberration correction element provided with an antireflection film, in which the transmittance of a light beam having a wavelength of 405 nm used in BD exceeds 80%. However, this aberration correction element not only has a transmittance of light beams with wavelengths of 780 nm and 658 nm used for CDs and DVDs of less than 88%, but also has a transmittance of light beam with a wavelength of 405 nm of less than 85%. It has never been. On the other hand, in the aberration correction element shown in FIGS. 14 to 17 described in the same document, the transmittances of light beams with wavelengths of 780 nm and 658 nm both exceed 93%. Taking this into consideration, the aberration correction element shown in FIG. 18 of the same document has a low transmittance over the entire wavelength region of 400 nm to 800 nm, and among them, the transmittance of the light beam near the wavelength of 405 nm is the same. Similar to the aberration correction element shown in FIGS. Judging from the above matters, it can be said that the aberration correction element shown in FIG. 18 of the same document is not suitable for compatibility with the three types of optical disks of CD, DVD, and BD.

  As described above, the reason why the aberration correction element is not compatible with the above three types of optical disks is largely derived from the fact that the transmittance of the light beam at the above three wavelengths in the antireflection film is not appropriate. is doing.

  The present invention has been made in view of the above circumstances, and has an appropriate compatibility for a plurality of types of optical discs by adding appropriate improvements to the antireflection film of an optical element such as an aberration correction element. In addition, an object of the present invention is to provide an optical pickup device that is excellent in alkali resistance, solvent resistance, NaCl resistance, moisture resistance, wear resistance, and reliability for evaluation tests for adhesion.

The antireflection film of the present invention created in order to solve the above technical problem is an antireflection film provided on an aberration correction element which is a constituent element of an optical pickup device, and is provided on at least a substrate of the aberration correction element. Four layers are formed. The four layers are, in order from the substrate side, a first layer having a refractive index nd of 2.0 or more and a geometric thickness of 5 to 50 nm, and a refractive index nd of 1. A second layer of 5 or less and a geometric thickness of 10 to 200 nm, a third layer of refractive index nd of 2.0 or more and a geometric thickness of 50 to 200 nm, and SiO ₂ or Al ₂ O ₃ or a fourth layer comprising SiON and having a geometric thickness of 50 to 200 nm. Here, the “geometric thickness” is distinguished from an optical thickness such as λ / 4, and is a thickness that does not depend on the wavelength. In addition, the above-mentioned “including SiO ₂ or Al ₂ O ₃ or SiON” means that these substances are included as main components.

  That is, according to the present invention, if the characteristic of the antireflection film provided in the aberration correction element is appropriate, the transmission characteristic of the light beam at a plurality of specific wavelengths in the aberration correction element is excellent. This has been devised by the knowledge of the present inventors. And according to said structure, since the reflectance of the light beam in wavelength 780nm, 658nm, and wavelength 405nm which are each used by CD, DVD, and BD is all provided 3% or less, It is possible to obtain an aberration correction element that is precisely compatible with the above three types of optical disks and excellent in reliability, and thus an optical pickup device. More specifically, if an anti-reflection film having a light beam reflectance of at least one of the three wavelengths above 3% is provided on the aberration correction element, at least one of the wavelengths is used. There is a possibility that the return light to the light source due to the reflection of the light beam cannot be appropriately reduced, or it is difficult to transmit the light beam without causing a loss. Therefore, if all the reflectances are 3% or less, such a problem is hardly caused. In consideration of this, it is more preferable that the above-mentioned reflectances are all 1% or less, and further all are 0.5% or less.

  When the four layers are formed as described above, the reflectance characteristics are suitably changed as compared with the case of the conventional single layer, and as already described, the wavelengths are 405 nm, 658 nm, and 780 nm. An antireflection film having a light beam reflectance of 3% or less (preferably 1% or less, more preferably 0.5% or less) can be obtained.

  Further, if four layers are formed as described above, the reflection prevention of the light beam reflectance in the wavelength region of 400 to 410 nm, 640 to 680 nm, and 760 to 800 nm is 3% or less (preferably 1% or less). A membrane can be obtained. By obtaining such an antireflection film, even if there is a variation in the wavelength of the light source or a wavelength shift of the reflected light from the optical disk, the aberration correction element can suitably transmit a light beam without causing an undue loss. It can be transmitted.

  In this case, in order to respond to a request to obtain an antireflection film having a light beam reflectivity that is as small as that of the above-described four layers in a plurality of specific wavelength ranges, the following configuration is used. You can also

  That is, at least five layers are formed on the substrate, and in addition to the first to fourth layers, the five layers have a refractive index nd of 1 between the substrate and the first layer. And a first inner layer having a geometric thickness of 10 to 150 nm.

  Further, at least six layers are formed on the substrate, and the six layers are arranged between the third layer and the fourth layer in addition to the first to fourth layers. In order from the side, a first outer layer having a refractive index nd of 1.5 or less and a geometric thickness of 10 to 150 nm, and a second outer layer having a refractive index nd of 2.0 or more and a geometric thickness of 10 to 200 nm. The outer layer is provided.

  Further, at least nine layers are formed on the substrate, and these nine layers are arranged in order from the substrate side between the substrate and the first layer in addition to the first to fourth layers. A first inner layer having a refractive index nd of 1.5 or less and a geometric thickness of 10 to 150 nm, and a second inner layer having a refractive index nd of 2.0 or more and a geometric thickness of 5 to 50 nm And a third inner layer having a refractive index nd of 1.5 or less and a geometric thickness of 10 to 100 nm, and in order from the substrate side between the third layer and the fourth layer. A first outer layer having a refractive index nd of 1.5 or less and a geometric thickness of 10 to 150 nm, and a second outer layer having a refractive index nd of 2.0 or more and a geometric thickness of 10 to 200 nm Be prepared.

In the above configuration, the layer having a refractive index nd of 2.0 or more is a layer containing TiO ₂ or Nb ₂ O _5, and the layer having a refractive index nd of 1.5 or less is SiO ₂ , MgF ₂ and A layer selected from CaF ₂ is preferred.

In the above configuration, the fourth layer can be the outermost layer. In such a case, if the fourth layer contains SiO ₂ as described above, it can serve as a protective film, and can have alkali resistance, solvent resistance, NaCl resistance, and It is possible to obtain an antireflection film excellent in moisture resistance.

  Further, each of the above layers can be formed as a sputtered film. In such a case, an antireflection film excellent in wear resistance and adhesion (or adhesion) can be obtained.

  The antireflection film described above is preferably provided on both the front and back surfaces of the aberration correction element in order to obtain good characteristics.

  In this case, the above antireflection film can be used for other optical elements instead of the aberration correction element of the optical pickup device. That is, the reflectance of the light beam when the wavelength is 405 nm, 658 nm and 780 nm, or the reflectance of the light beam when the wavelength region is 400 to 410 nm, 640 to 680 nm and 760 to 800 nm is a small value as described above. As long as the optical element is required to show the above, the above-described antireflection film may be provided not only on the aberration correction element but also on other optical elements.

  Moreover, the antireflection film described above can be provided on a glass plate (for example, the surface of a glass plate used as all or part of an optical element) and provided as a glass article.

  As described above, according to the antireflection film according to the present invention, the reflectance of the light beam at three wavelengths or three wavelength regions respectively used for CD, DVD, and BD is appropriately reduced. It is possible to obtain an optical element having an appropriate compatibility with the three types of optical disks and having excellent reliability, and thus an optical pickup device, which is extremely advantageous for improving convenience. In addition, the optical element provided with the antireflection film can appropriately reduce the return light to the light source due to the reflection of the light beams of the three wavelengths, and those light beams can be generated without causing undue loss. Can be transmitted satisfactorily, and high-quality optical characteristics can be obtained.

It is the schematic which shows an example of the optical pick-up apparatus which uses the aberration correction element provided with the antireflection film based on embodiment of this invention as a component. It is the schematic which shows the structure of four types of antireflection film which concerns on embodiment of this invention. It is a graph which shows the characteristic of the anti-reflective film (1st and 2nd example) which concerns on embodiment of this invention. It is a graph which shows the characteristic of the anti-reflective film (3rd example) which concerns on embodiment of this invention. It is a graph which shows the characteristic of the anti-reflective film (4th example) which concerns on embodiment of this invention.

  Embodiments of the present invention will be described below with reference to the accompanying drawings.

  FIG. 1 is a schematic view showing an example of an optical pickup device having an aberration correction element provided with an antireflection film according to an embodiment of the present invention as a constituent element. As shown in the figure, this optical pickup device 1 includes a semiconductor laser 2, a beam splitter 3, a magnification conversion mechanism 4, a mirror 5, an aberration correction element (liquid crystal element) 6, an NA control element 7, and a quarter wavelength plate 8. , Objective lens 9 and photodetector 10. Then, the light beam L emitted from the semiconductor laser 2 passes through the beam splitter 3, is converted into parallel rays by the magnification conversion mechanism 4, further passes through the aberration correction element 6, and the like, and is transmitted through the objective lens 9 to the optical disk D. Focused on the recording surface. The light beam L reflected from the recording surface of the optical disc D is incident on the beam splitter 3 again, and then the optical path is bent and guided to the photodetector 10 for predetermined detection.

  In this case, the light beam L is transmitted through the aberration correction element 6 to correct spherical aberration and the like. The antireflection film as shown below is provided on both the front and back surfaces or one surface of the aberration correction element 6. Is provided.

That is, as a first example, the four-layer antireflection film described in the column denoted by reference numeral 40 in FIG. 2 is provided on one side of the base of the aberration correction element 6 (for example, a glass base disposed on the front and back of the element 6). It is formed by sputtering on the surface on which the light beam is incident. More specifically, the four-layer antireflection film has, in order from the substrate side, a first layer having a geometric thickness of 24 nm and made of TiO _2, and a geometric thickness of 33 nm and made of SiO _2. A second layer, a third layer having a geometric thickness of 111 nm and made of Nb ₂ O _5, and a fourth layer (outermost layer) having a geometric thickness of 119 nm and made of SiO ₂ Formed. In this case, the refractive index nd of TiO ₂ is 2.32, the refractive index nd of SiO ₂ is 1.47, and the refractive index nd of Nb ₂ O ₅ is 2.20.

  FIG. 3 shows that the inventors formed the above four-layer antireflection film on a borosilicate glass substrate (refractive index nd is 1.52) by sputtering, and measured the reflectance of the antireflection film. It is a graph which shows the reflectance curve 4A obtained by measuring. The reflectance is a value measured with a spectrophotometer after the light beam is incident from the fourth layer (outermost layer). As can be generally understood from the reflectance curve 4A shown in FIG. 3, the reflectance of the light beam at the wavelength of 405 nm is 0.04%, the reflectance of the light beam at the wavelength of 658 nm is 0.03%, and the reflectance at the wavelength of 780 nm. The reflectance of the light beam was 0.05% (see the column denoted by reference numeral 40 in FIG. 2).

Next, as a second example, the five-layer antireflection film described in the column denoted by reference numeral 50 in FIG. 2 has a geometric thickness of 50 nm on one side of the base of the aberration correction element 6 in order from the base. A first inner layer made of SiO ₂ , a first layer made of TiO ₂ with a geometric thickness of 24 nm, a _second layer made of SiO ₂ with a geometric thickness of 35 nm, A third layer made of Nb ₂ O ₅ with a geometric thickness of 111 nm and a fourth layer (outermost layer) made of SiO ₂ with a geometric thickness of 117 nm were formed by sputtering. Is.

  Here, the present inventors have formed a five-layer antireflection film in the same procedure as in the first example, and the reflectance curve obtained by measuring the reflectance of the antireflection film is: This is substantially the same as the curve 4A shown in FIG. The five-layer antireflection film has a light beam reflectance at a wavelength of 405 nm of 0.02%, a light beam reflectance at a wavelength of 658 nm of 0.03%, and a light beam reflectance at a wavelength of 780 nm. Was 0.05% (see the column denoted by reference numeral 50 in FIG. 2).

Further, as a third example, the six-layer antireflection film described in the column denoted by reference numeral 60 in FIG. 2 has a geometric thickness of 7 nm on one side of the base of the aberration correction element 6 in order from the base. A first layer made of Nb ₂ O _{5, a second} layer made of SiO ₂ with a geometric thickness of 163 nm, and a third layer made of Nb ₂ O ₅ with a geometric thickness of 160 nm A first outer layer made of SiO ₂ with a geometric thickness of 119 nm, a second outer layer made of Nb ₂ O ₅ with a geometric thickness of 147 nm, and a geometric thickness of 58 nm Thus, a fourth layer (outermost layer) made of SiO ₂ is formed by sputtering.

  FIG. 4 shows a reflectance curve 6A obtained by the inventors forming a six-layer antireflection film and measuring the reflectance of the antireflection film in the same procedure as in the first example. It is a graph which shows. As can be generally understood from the reflectance curve 6A shown in FIG. 4, the reflectance of the light beam at a wavelength of 405 nm is 0.05%, the reflectance of the light beam at a wavelength of 658 nm is 0.22%, and the reflectance at a wavelength of 780 nm. The reflectance of the light beam was 0.04% (see the column denoted by reference numeral 60 in FIG. 2).

As a fourth example, the nine-layer antireflection film described in the column denoted by reference numeral 90 in FIG. 2 has a geometric thickness of 99 nm on one side of the base of the aberration correction element 6 in order from the base. A first inner layer made of SiO _{2, a second} inner layer made of TiO ₂ with a geometric thickness of 7 nm, a third inner layer made of SiO ₂ with a geometric thickness of 47 nm, A first layer having a geometric thickness of 21 nm and made of Nb ₂ O _{5, a second} layer having a geometric thickness of 31 nm and made of SiO _2, and a geometric thickness of 79 nm and Nb ₂ A third layer made of O _{5, a} first outer layer having a geometric thickness of 16 nm and made of SiO _{2, a second} outer layer made of Nb ₂ O ₅ and having a geometric thickness of 22 nm, and a fourth layer geometrical thickness of SiO ₂ to a 101 nm (outermost layer), scan Tsu is obtained by forming by another method.

  FIG. 5 shows a reflectance curve 9A obtained by the inventors forming a nine-layer antireflection film and measuring the reflectance of the antireflection film in the same procedure as in the first example. It is a graph which shows. As can be generally understood from the reflectance curve 9A shown in FIG. 5, the reflectance of the light beam at the wavelength of 405 nm is 0.05%, the reflectance of the light beam at the wavelength of 658 nm is 0.18%, and the reflectance at the wavelength of 780 nm. The reflectance of the light beam was 0.23% (see the column denoted by reference numeral 90 in FIG. 2).

  According to the reflectance curves 4A, 6A, and 9A of the antireflection films of four layers, five layers, six layers, and nine layers shown in FIGS. 3 to 5 above, the optical disc D is used for CD, DVD, and BD, respectively. The reflectances of the light beams at the wavelengths of 780 nm, 658 nm, and 405 nm are all 3% or less (the experimental value is 0.25% or less). In addition, the reflectance of the light beam in the wavelength region of 400 to 410 nm, 640 to 680 nm, and 760 to 800 nm is all 3% or less (experimental value is 0.8% or less). Therefore, it can be seen that the aberration correction element 6 in which these antireflection films are formed on both the front and back surfaces has accurate compatibility with the above three types of optical disks.

  Furthermore, the present inventors, for the borosilicate glass substrate (hereinafter referred to as a sample) formed with each of the antireflection films, alkali resistance, solvent resistance, NaCl resistance, moisture resistance, wear resistance, When the adhesiveness evaluation test was performed, all passed.

  For alkali resistance, the sample was immersed in a 3% KOH aqueous solution for 10 minutes, and for solvent resistance, the sample was immersed in acetone at room temperature for 20 minutes, and the reflectance of each sample at that time was a wavelength of 405 nm ± 10 nm. When the wavelength was 658 nm ± 25 nm and the wavelength was 780 nm ± 25 nm and the ratio was 0.5% or less, and there were no film peeling, cracks, and spots, the test was accepted. As for NaCl resistance, in accordance with MIL-C-675 3.8.1, after immersing the sample in a NaCl solution for 24 hours, film deterioration such as film chipping, peeling, cracks, and bubbles was observed. Otherwise, it was accepted. Further, regarding abrasion resistance, the sample was rubbed for 50 strokes with an eraser applied with a load of about 1.0 kg in accordance with KIL-C-675 3.8.4, and then the film was not peeled off and dried. After rubbing the sample with clean cotton (Ben cotton), if the film did not peel off, the sample was accepted. In addition, regarding moisture resistance, according to MIL-C-675 3.8.2, the sample was exposed to an atmosphere of 95% to 100% humidity at 48.9 ± 2.2 ° C. for 24 hours, and then the film chipped or peeled. The film was evaluated as acceptable on the condition that the film did not deteriorate, such as cracks and bubbles, and passed the above abrasion resistance. Furthermore, regarding adhesion, according to MIL-C-675 3.8.5, Nichiban Cello Tape (registered trademark) # 405 (manufactured by Nichiban Co., Ltd.) was attached to the sample, and the film was peeled off when peeled three times. If there is no, it was accepted.

  In the above embodiment, the antireflection film according to the present invention is provided in the aberration correction element of the optical pickup device. However, the reflectance of the light beam at wavelengths of 405 nm, 658 nm, and 780 nm, or the wavelength region. However, as long as the optical element is required to have a low light beam reflectance at 400 to 410 nm, 640 to 680 nm, and 760 to 800 nm as described above, the present invention can be applied to other optical elements. Such an antireflection film may be provided.

  The antireflection film according to the present invention can be used for an aberration correction element (for example, a hologram element) compatible with CD, DVD, and BD, and is required to exhibit the same function and effect. Can also be used.

1 Optical pickup device 6 Aberration correction element (optical element)
40 Four-layer antireflection film 50 Five-layer antireflection film 60 Six-layer antireflection film 90 Nine-layer antireflection film

Claims (9)

An antireflection film provided on an aberration correction element that is a component of an optical pickup device,
At least four layers are formed on the base of the aberration correction element. The four layers are, in order from the base, the first refractive index nd of 2.0 or more and the geometric thickness of 5 to 50 nm. A second layer having a refractive index nd of 1.5 or less and a geometric thickness of 10 to 200 nm, and a third layer having a refractive index nd of 2.0 or more and a geometric thickness of 50 to 200 nm. An antireflection film comprising: a layer; and a fourth layer containing SiO _2, Al ₂ O _3, or SiON and having a geometric thickness of 50 to 200 nm.   At least five layers are formed on the substrate, and in addition to the first to fourth layers, the five layers have a refractive index nd of 1.5 between the substrate and the first layer. The antireflection film according to claim 1, further comprising a first inner layer having a geometric thickness of 10 to 150 nm.   At least six layers are formed on the substrate, and these six layers are arranged between the third layer and the fourth layer in addition to the first to fourth layers from the substrate side. In order, a first outer layer having a refractive index nd of 1.5 or less and a geometric thickness of 10 to 150 nm, and a second outer layer having a refractive index nd of 2.0 or more and a geometric thickness of 10 to 200 nm. The antireflection film according to claim 1, wherein the antireflection film is provided.   At least nine layers are formed on the substrate, and these nine layers are refracted in order from the substrate side between the substrate and the first layer in addition to the first to fourth layers. A first inner layer having a refractive index nd of 1.5 or less and a geometric thickness of 10 to 150 nm; a second inner layer having a refractive index nd of 2.0 or more and a geometric thickness of 5 to 50 nm; A third inner layer having a ratio nd of 1.5 or less and a geometric thickness of 10 to 100 nm, and being refracted in order from the substrate side between the third layer and the fourth layer. A first outer layer having a refractive index nd of 1.5 or less and a geometric thickness of 10 to 150 nm; and a second outer layer having a refractive index nd of 2.0 or more and a geometric thickness of 10 to 200 nm. The antireflection film according to claim 1, wherein the antireflection film is provided. The layer having a refractive index nd of 2.0 or more is a layer containing TiO ₂ or Nb ₂ O _5, and the layer having a refractive index nd of 1.5 or less is selected from SiO ₂ , MgF ₂ and CaF _2. The antireflection film according to claim 1, wherein the antireflection film is a layer.   The antireflection film according to claim 1, wherein the fourth layer is an outermost layer.   The antireflection film according to claim 1, wherein the antireflection film is provided on both front and back surfaces of the aberration correction element.   8. The antireflection film according to claim 1, wherein the antireflection film according to claim 1 is provided on another optical element instead of the aberration correction element.   A glass article, wherein the antireflection film according to any one of claims 1 to 8 is provided on a glass plate.

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